1. Field of the Invention
The invention relates to highly sulfurized molybdenum oxysulfide dithiocarbamate compounds and processes for preparing same.
2. Discussion of the Prior Art
Molybdenum oxysulfide dithiocarbamates have been added to greases and lubricating oils for many years in order to improve extreme pressure properties, antiwear properties, antioxidancy, and for friction modification. There have been many methods described in the patent literature to prepare such materials.
U.S. Pat. No. 3,356,702 from Farmer et al. describes a method to prepare sulfurized molybdenum oxysulfide dithiocarbamates by solubilizing MoO3 in water with an alkali metal hydroxide or ammonium hydroxide followed by neutralization with a mineral acid, then addition of CS2 and a secondary amine.
U.S. Pat. No. 3,356,702 also describes a method in which MoO3 or MoO2 is placed in a polar solvent and the secondary amine and CS2 are then added. Best results are obtained when at least 1.5 equivalents of amine relative to Mo are added to the reaction. This represents at least a 33% excess of amine. Sulfur levels are commonly around 25% by weight when the secondary amine used is dibutylamine.
U.S. Pat. No. 4,098,705 from Sakurai et al. describes a method to prepare highly sulfurized molybdenum oxysulfide dithiocarbamates by reacting a hexavalent molybdenum source with an alkali sulfide such as NaSH or Na2S, followed by neutralization with a mineral acid, and addition of secondary amine and CS2. Based on the elemental analyses in the examples, the material formed is highly sulfurized, between 27 and 30% sulfur by weight when the secondary amine used is dibutylamine. U.S. Pat. No. 5,631,213 from Tanaka et al. describes a method to prepare a highly sulfurized molybdenum oxysulfide dithiocarbamate similar to U.S. Pat. No. 4,098,705, but with the addition of a reducing agent.